A hydroformylation reaction in which an olefin reacts with a synthesis gas (CO/H2) in the presence of a homogeneous organicmetallic catalyst and a ligand to produce linear (normal) and branched (iso) aldehyde which has one more carbon atom than olefin was originally discovered by Otto Roelen in Germany in 1938.
In general, the hydroformylation that is known as an oxo reaction is a very important industrial reaction in views of a homogeneous system catalyst reaction, and currently, about 9,600,000 tons of aldehydes (including alcohol derivatives) are produced by the oxo process and consumed all over the world (SRI report, September 2006, 682. 7000 page 7).
Various types of aldehydes produced by the oxo reaction are oxidized to carboxylic acids or hydrogenated to alcohols. In addition, aldehydes can also be converted to long alkyl chain-containing acids or alcohols through aldol condensation and then oxidation or reduction. In particular, hydrogenated alcohol of aldehyde, which is obtained by the oxo reaction, is called oxo alcohol. Oxo alcohol is industrially extensively used as a solvent, an additive, various types of raw materials of plasticizers, synthesis lubricants, and chemical intermediates.
It is known that a metal carbonyl hydride compound has a catalytic activity of the hydroformylation reaction. The N/I (ratio of linear (normal) to branched (iso) isomers) selectivity of aldehydes varies according to the type of ligand used and operating conditions.
Modern hydroformylation research is almost exclusively focused on cobalt(Co), rhodium(Rh), platinum(Pt) and ruthenium(Ru) metal catalyst. In respects to the transition metals, it is known that the order of the catalytic activity is Rh>>Co>Ir, Ru>Os>Pt>Pd>Fe>Ni. Platinum and ruthenium catalyst are mainly subjects of academic interest. Therefore, cobalt and rhodium catalysts have been mainly used in an oxo process. To date, a rhodium-based low-pressure oxo process (LPO Process) has been adopted in at least 70% of oxo plants worldwide because of the high efficiency, high yield of normal products, and mild reaction condition even though there are disadvantages of the expensive catalyst and catalytic deactivation due to the poisoning.
Examples of the ligand that is used during the oxo process include phosphine (PR3, R═C6H5, and n-C4H9), phosphine oxide, and phosphite. In the case of when rhodium is used as the central metal, it is known that the ligand having the catalytic activity and the stability that are better than those of triphenylphosphine (TPP) is almost not present. Thus, in most oxo process, Rh metal is used as a catalyst and TPP is used as a ligand. In addition, to increase the stability of a catalytic system, TPP ligand is used in an amount of at least 100 equivalent of the catalyst.
In general, since the value of the linear aldehyde derivative is high among aldehydes that are products of the oxo reaction, many studies have been made to increase the ratio of the linear aldehyde in respects to the catalyst. However, recently, products obtained by using iso-aldehyde as the raw materials instead of the linear aldehyde, for example, an isobutyric acid, neopentyl glycol (NPG), 2,2,4-trimethyl-1,3-pentanediol, an isovaleric acid and the like have been developed, thus the use of iso-aldehyde has been increased. Accordingly, there is a demand to develop a technology of producing normal- and iso-aldehyde required in a market by desirably controlling the N/I selectivity while the excellent catalytic activity is maintained.